Manganese‐Release Characteristics of Highly Calcareous Soils

Abstract

Manganese (Mn) deficiency is common in calcareous soils of southern Iran. The ability of these soils to replenish the soil solution Mn depends highly on their Mn‐release characteristics. Kinetics of native Mn release by ammonium bicarbonate diethylenetriaminepentaacetic acid (AB‐DTPA) from 10 highly calcareous soils were studied for the periods of 1 to 1440 min. Results showed that Mn‐release rates were initially fast, followed by a much slower rate. Among seven kinetic models tested, two constant‐rate, simple Elovich, and parabolic diffusion models best predicted the pattern of time‐dependent Mn release well, much better than zero‐, first‐, second‐, and third‐order models. Significant correlations were observed between constant values of parabolic diffusion with those of simple Elovich model (Kp and Q₀ with β _s and α _s, respectively), which demonstrated that Mn release from calcareous soils of southern Iran is probably a diffusion‐controlled process. Results of stepwise regression analysis between constant values of the best‐fitted models and selected soil properties showed that the content of easily reducible Mn oxides (ERMn) was the only soil property capable of predicting some constant values of the best‐fitted models. According to the equations, Mn‐release rates increased as the amount of ERMn increased. It is therefore concluded that ERMn is probably the main source of Mn release in these calcareous soils. Further research to assess the relationships of constant values of the best‐fitted models with plant growth parameters in calcareous soils is warranted.

Keywords:

• AB‐DTPA
• calcareous soils
• easily reducible Mn
• kinetics
• release

ACKNOWLEDGMENT

The authors thank Shiraz University for providing research facilities. We thank Mr. Nouri for his help collecting soil samples.